An engine lathe is a machine in which a piece of metal to be worked is rotated about a horizontal axis and is shaped by contact with a fixed cutting, boring or drilling tool. For manual machine operations, the tools are normally held by a tool holder that is attached to a sliding bed that is movable in two dimensions. The tool holder is positioned such that the center of the tool coincides with the centerpoint of the spindle of the lathe. The centered position is the reference point, and all measurements of the movements of the bed in either the X or Y direction are made relative to the reference point. In this manner the movement of the tool holder can be measured and controlled to provide for accurate cutting, drilling, and boring. A rotating turret is a tool holder for use with an engine lathe and that typically has six to eight (more or less are possible) tool positions that can be rotated in order to switch from one tool to another. For a rotating turret one of the tool holders is positioned to correspond with the centerpoint of the spindle of the lathe and as a result all of the tools are on center when rotated into this position.
The rotating turret enables the machinist to make use of several tools for changes "on the fly" without having to remove and replace the tools in a single head on the tool holder. In rotating turret systems, the turret is disengaged from its locked position, rotated into the desired position, and then placed in the locked position again.
In order to provide for indexing between different tool positions on a rotating turret, a device must provide for locking and unlocking of the rotating turret and for rotation of the turret. The existing systems, such as the Dorian VIT available from Dorian Tool in Houston, Tex., usually provide for locking and unlocking the turret by means of a set of interlocking gear plates. The gear plates may be spline gears or other types of gear faces that bring together several surfaces to prevent relative rotation between the plates. In order to disengage the locking mechanism, one of the plates has to be retracted. Some of the existing systems require the steps of: rotating the knurled handle in order to disengage the gear plates, rotating the turret into the next position and then rotating the knurled handle again to lock the turret into the next position. These steps can become very tedious when several tool changes are required.
Once the locking mechanism is disengaged, the movement of the turret is usually restrained in some manner. If the turret is allowed to spin freely once the locking mechanism is disengaged, the weight of the tools may cause them to rotate unexpectedly and to cause damage to the work or the operator. Many of the existing systems do not adequately protect the work from damage due to inadvertent rotation of the turret when the locking mechanism is disengaged.
The movement of the turret between the different tool positions is accomplished in several different ways in the existing systems. Some systems require manual indexing by unlocking the turret and manually rotating the turret between tool positions. Other systems provide for automatic indexing through the use of compressed air. The air systems are not completely satisfactory because they can be quite cumbersome and require a lot of space that may not be available in all instances and especially for retrofitting to existing lathes.
Switching tools and indexing a turret with the existing systems has generally not been as efficient and easy as it should be because of the requirements and limitations of the rotating turret designs discussed above. What is needed is a rotating turret for an engine lathe that provides a quick and user friendly locking mechanism, improves the method of engaging and disengaging the locking mechanism, employs a locking mechanism that provides rigidity and stability to the tools, provides protection for the work when the locking mechanism is disengaged, and provides a low maintenance, durable design for a rotating turret.